Video displays are almost always provided at data processing system work stations in order to provide a visual representation of the information being processed at any given instant. Most video displays have a cathode ray tube (CRT) to generate images of the information they are designed to display. Cathode ray tubes are large vacuum tubes that have a flat surface at one end that serves as a screen face, and taper into a cylindrical neck at the opposite end. A phosphorous coating is applied to the inside of the screen face, and an electron-emitting source, an electron gun, is housed in the neck of the tube and pointed toward the screen face. The electron gun is triggered to selectively emit electrons by a video drive circuit located external to the CRT. The electrons strike the phosphorous on the screen face, and excite it so light is momentarily emitted. The light emitted by the CRT is the visual image generated by the video display.
Recent advances in CRT technology and video drive circuit technology have made the development of ultra high resolution video display terminals possible. These terminals are able to generate images with exceedingly fine detail and shading that was previously difficult to display. Moreover, many video terminals currently being produced are able to generate color displays. The ultra high resolution CRTs are able to blend the three primary colors, which is typically what the electron gun, or set of guns inside the CRT, generate, into a very large spectrum of intermediate colors for display.
The new ultra high resolution video display terminals have become very useful because they can produce very complicated representations of the information being processed by the data processing system. Moreover, these video displays can be incorporated into a desk-top publishing system that, with the use of an appropriate printer, can be used to generate quantities of documents that include both textual and image material. An ultra high resolution display is an integral part of a desk-top publishing system because it can be used to display what material will be printed before the actual printing process is performed.
To date, however, there have been problems associated with connecting the cathode ray tube of ultra high resolution video display terminals to their associated video amplifier circuits. The video amplifier circuit of a video display terminal supplies the necessary signal voltages to the CRT to drive the electron gun or guns therein. In the past, video amplifier circuits have been on a circuit board, called the "video board", that is attached to the CRT. Conductive leads connected between the video board to a socket coupled to contact pins on the CRT would serve as the paths for signals transmitted to the CRT. In some instances, the socket was mounted directly to the video board, and in other instances, a hole was formed in the video board and the video board disposed around the end of the CRT.
Problems have arisen because ultra high resolution CRTs require CRT drive signals that are at very high frequencies in order to generate the desired detailed images. As the high frequency signals are forwarded to the CRT, the CRT inherently acts as a capacitor, and the conductive path to it inherently acts as an inductor. This results in the filtering and distortion of signals forwarded to the CRT, consequently the images generated by the CRT are subject to degradation.
Another problem associated with ultra high resolution video displays is that the video amplifier operates at a relatively high power level and transmits voltages to the CRT at very high frequencies. Consequently, the video amplifier in effect is a generator of spurious electromagnetic waves that could effect the operation of other nearby electronic devices. This is especially true if the video display terminal is adjacent other data processing devices that also operate at relatively high speeds and hence may be effected by even minute inductive currents generated by stray electromagnetic waves.
Another consideration in the design of an ultra high resolution video display terminal is the heat generated by their video amplifiers. Ultra high resolution video display video amplifiers generate large amounts of heat as a consequence of the large amounts of power they consume in order to provide the necessary video drive signals to the CRT. If the heat generated by the video amplifier circuit is not dissipated therefrom, the components that comprise the circuit may overheat resulting in their malfunction or possible burnout.